A large quantity of moisture-containing exhaust gas may be produced during a process of drying, pyrolysis or the like. Said moisture-containing exhaust gas generally contains a large amount of moisture (including inorganic moisture such as water vapor; or organic moisture such as hexane, methanol, ethanol, and/or acetic acid, etc) and a small amount of solid dust from the process of drying, pyrolysis or the like. It is a conventional technique to dehumidify the moisture-containing exhaust gas with a dehumidifying tower, such as a washing and cooling tower, to remove the moisture therein, which has been applied widely in process industries such as chemical industry (e.g., petrochemical industry, coal chemical industry, etc.), steel industry, metallurgy industry and the like.
FIG. 1 shows a conventional washing and cooling tower 90, which from top to bottom comprises: a gas outlet 901, a gas demister 902, a liquid distributor 903, a filling unit 904 filled with one or more layers of fillers, a gas inlet distributor 905, a liquid overflow discharge device 906 and a liquid storage region 907 at a lower part of the tower, and a liquid outlet 908 at the bottom of the tower.
As shown in FIG. 2, a moisture-containing exhaust gas from for example the drying process enters the washing and cooling tower 90 from a gas inlet 909 near the bottom of the tower, and rises to the filling unit 904. A circulating cooling liquid condensed from the moisture enters the tower from its top, and is evenly sprayed onto the surface of the underlying filler layer through the liquid distributor 903. In the filler layer, heat exchange and mass exchange proceed between the moisture-containing exhaust gas and the circulating cooling liquid, which contact with each other in a counter-flowing manner. During this process, the moisture-containing exhaust gas is cooled by the circulating cooling liquid, so that at least a portion of moisture in the exhaust gas is condensed into liquid and joins becomes a portion of the circulating cooling liquid; while the exhaust gas is washed by the circulating cooling liquid, so that the solid dust in the exhaust gas is at least partially removed therefrom. After passing through the filling unit 904, the exhaust gas continues to rise in the tower. After demisted by the demister 902, the exhaust gas is discharged from the washing and cooling tower 90 via the gas outlet 901 by an induced draft fan 912. During the above-mentioned exchanging processes, the circulating cooling liquid is heated by the exhaust gas. The circulating cooling liquid that leaves the filler layer falls to the bottom of the tower. A portion of the circulating cooling liquid is discharged through the overflow discharge device 906 or a circulating cooling liquid pump 910 at the bottom of the tower, and becomes a recycled moisture liquid consisting of the moisture and the dust. The remaining circulating cooling liquid is discharged from the tower via the liquid outlet 908 by the circulating liquid pump 910 at the bottom of the tower, and then fed into a cooling device 920 for cooling. The cooled cooling liquid is fed again into the washing and cooling tower 90 to repeat the above processes.
However, such cooling tower in the prior art suffers from the following drawbacks.
The recycled moisture liquid obtained from the washing and cooling tower includes not only the liquid condensed from the moisture in the exhaust gas, but also solid dust entrained in the exhaust gas. Thus, a further liquid-solid separation process is required to be performed on the recycled liquid, which is technically complicated and costly.
Furthermore, the dust entrained in the moisture-containing exhaust gas may also enter the circulating cooling liquid, which tends to block the cooling device block during the cooling process for the cooling liquid, and lower the heat exchanging efficiency.
Moreover, a washing, cooling, and recycling process with using said conventional washing and cooling tower 90 requires a great number of other apparatuses or devices, and requires large work area.